1. Field of the Invention
The present invention relates to a switch for detecting an idle position of an internal combustion engine.
2. Discussion of Background
An idle position detecting switch is used in an internal combustion engine in case that a control is required, for example, as to a fuel supply amount in accordance with a degree of opening of a throttle valve.
An example of such conventional idle position detecting switches is shown in FIG. 5. In FIG. 5, internally arranged in a cylindrical housing fixed to a throttle body 1 are a push rod 3, a movable contact 4 disposed at the lower end portion of the push rod 3, and a fixed contact 5 opposing the movable contact 4. The throttle body 1 is fixed to the engine (not shown) and thus grounded therethrough. The push rod 3 ia slidably fitted inside a small diameter portion 6a of a cylindrical guide 6 set in the housing 2. The upper end portion of the push rod projects from an opening at the upper end of the housing 2. A ring plate 7 fits around the lower end portion of the push rod 3 inside a large diameter portion 6b of the guide 6. A cylindrical insulator 8 is disposed inside the lower opening portion of the housing 2. A large diameter portion 8a of the insulator 8 fits in an inner circumference of the housing 2. A small diameter portion 8b of the insulator 8 fits around the lower end portion of the push rod 3. A lead plate 7a is interposed between the lower end face of the large diameter portion 6b of the guide 6 and an end face of the large diameter portion 8a of the insulator 8. A spring 9 is interposed as an electric member between the plate 7 and the lead plate 7a. Consequently, the push rod 3 is always urged by the spring 9 toward a pivoting end portion 20a of a stopper 20 linked to a valve shaft 19 of the throttle valve. The push rod 3 is slidable against the elastic force of the spring 9 by being pushed by the stopper 20. A terminal 14 is connected to the fixed contact 5 and guided to the outside through a resinous connector 11 set inside the lower end opening of the housing 2. The connector 11 is fixedly held in the housing 2 by caulking a portion 2b which extends from the lower end opening of the housing 2. The housing 2 has a threaded portion 2a on the upper periphery of the housing 2. The threaded portion 2a meshes with a female screw 1a threaded in the throttle body 1. A numeral 17 represents a rubber seal mounted over the upper end periphery of the housing 2.
There will be described an operation of the above-described switch.
When the valve shaft 19 of the throttle valve rotates in response to full closing of the throttle valve, the push rod 3 is pushed against the elastic force of the spring 9 by the pivoting end portion 20a of the stopper 20. As a result, the movable contact 4 provided at the lower end of the push rod 3 comes in contact with the fixed contact 5. The stopper 20 is positioned at this stage. The electric current from the terminal 14 is transmitted through the fixed contact 5, the push rod 3, the plate 7, the spring 9, the lead plate 7a, the housing 2 and the throttle body 1 to the earth, enabling the detection of the idle position.
In such conventional idle position detecting switch, the spring 9 for electric communication between the plate 7 and the lead plate 7a simply touches the plates 7, 7a at both ends thereof. The simple pressing arrangement of the spring 9 causes contact resistance. The contact resistance results in insufficient output of the detection signal. This tendency may be aggravated by oil adhesion onto and/or oxidation of the contacting surfaces. Further, if the spring 9 rotates in between the plates 7, 7a to change its contacting surfaces, the detection signal differs depending on contact position due to the same reason, causing instability of detection in the conventional switch.
Inventors of the present invention have invented such arrangement that the both ends of the spring 9 are fixed to respectively corresponding members, and filed a Japanese Utility Model Application No. 203257/1986, on Dec. 26, 1986. The inventors also filed U.S. patent application Ser. No. 137,580, filed Dec. 24, 1987 now Patent No. 4,815,317 claiming the priority based on the aforementioned Japanese application. assigned to the U.S. patent application, now copending with the present application.
As discussed in U.S. Pat. No. 4,815,317, since the both ends of the spring are fixed, the contact resistance thereat may be reduced, providing a stable signal. The arrangement is detailed below in reference to FIG. 4. Explanation will be simplified by showing the same elements with the same symbols as the arrangement in FIG. 5. The above description as to the same elements is incorporated herewith. A numeral 12 denotes a fixing ring disposed at the lower end of the push rod 3, numeral 13 a support disk carrying the fixed contact 5, a numeral 14 a terminal piece electrically connecting to the fixed contact 5 supported by the support disk 13, and a numeral 15 an end of a lead wire caulked with the terminal piece 14. A symbol 2c represents a step portion formed in the lower opening of the housing 2.
The upper end of the spring 9 has a small winding portion 9a extending radially inward and fitting around the small diameter portion at the lower end of the push rod 3. When the fixing ring 12 is secured to the lower end of the push rod 3, the small winding portion 9a is held between the ring 12 and the plate 7. Thus, the upper end of the spring 9 is electrically connected securely to the movable contact 4. The lower end portion of the spring 9 has a large winding portion 9b extending radially outward. The large winding portion 9b is located in a guide groove 8e arranged about the periphery of the insulator 8, and pinched by the insulator 8 and the step portion 2c of the housing 2 therebetween. In this way, the lower end of the spring 9 is electrically connected firmly to the housing 2. The pinching of the both ends of the spring 9 is simultaneously effected when the connector 11 is fixedly held by the housing 2 by caulking the portion 2b thereof.
A radially outwardly extending part of the lower end portion of the spring 9 passes through a recessed portion 8d to connect to the large winding portion 9b outside the recessed portion 8d. The insulator 8 has the guide groove 8e about its periphery as described before. The insulator 8 further has a post 8c opposite to the recessed portion 8d with respect to the center. The large diameter portion 6b of the guide 6 faces the insulator 8, so that the guide 6 and insulator 8 substantially enclose the spring 9 and the movable contact 4. The large diameter portion 6b has a cut 6c for receiving the post 8c of the insulator 8. The cut 6c is further engaged with a projection 7b radially extending from the plate 7, to be movable in the axial direction.
A wave washer 16 is disposed between the housing 2 and the large diameter portion 6b of the guide 6. A numeral 18 denotes a rubber cover surrounding the connector 11.
According to the above-described arrangement disclosed in U.S. Pat. No. 4,815,317, the plate 7 electrically connected to the movable contact 4 may be kept in secure electric communication with the housing 2, that is, in a state to be grounded through the spring 9.
However, the arrangement as shown in FIG. 4 has drawbacks as described below. In the arrangement, inserted in the housing 2 are the guide 6, the push rod 3 with the spring 9, and the insulator 8 in a consecutive order. The fixed contact 5 is placed on the connector 11. After that, the housing 2 and the connector 11 are assembled together and incorporated with each other by the caulking of the portion 2b of the housing 2. It is difficult to confirm that the part of the spring 9 radially outwardly extending to the large winding portion 9b just passes through the recessed portion 8d formed on the insulator upon the assembling of the housing 2 and the connector 11 with the insulator 8 interposed therebetween. There is discovered such a problem that the radially outwardly extending part of the spring 9 does not always pass through the recessed portion 8d of the insulator 8 and is often nipped by plain ends of the guide 6 and the insulator 8. Such nipping contact easily be found upon the assembling. Also, the assembling requires much time, resulting in lowering of productivity.